/*

 * Licensed to the Apache Software Foundation (ASF) under one

 * or more contributor license agreements.  See the NOTICE file

 * distributed with this work for additional information

 * regarding copyright ownership.  The ASF licenses this file

 * to you under the Apache License, Version 2.0 (the

 * "License"); you may not use this file except in compliance

 * with the License.  You may obtain a copy of the License at

 *

 *     http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

package com.bff.gaia.unified.sdk.coders;



import com.bff.gaia.unified.sdk.util.common.ElementByteSizeObserver;

import com.bff.gaia.unified.sdk.values.TypeDescriptor;

import com.bff.gaia.unified.sdk.values.TypeParameter;

import com.bff.gaia.unified.vendor.guava.com.google.common.collect.Maps;



import java.io.*;

import java.util.*;

import java.util.Map.Entry;



/**

 * A {@link Coder} for {@link Map Maps} that encodes them according to provided coders for keys and

 * values.

 *

 * @param <K> the type of the keys of the KVs being transcoded

 * @param <V> the type of the values of the KVs being transcoded

 */

public class MapCoder<K, V> extends StructuredCoder<Map<K, V>> {

  /** Produces a MapCoder with the given keyCoder and valueCoder. */

  public static <K, V> MapCoder<K, V> of(Coder<K> keyCoder, Coder<V> valueCoder) {

    return new MapCoder<>(keyCoder, valueCoder);

  }



  public Coder<K> getKeyCoder() {

    return keyCoder;

  }



  public Coder<V> getValueCoder() {

    return valueCoder;

  }



  /////////////////////////////////////////////////////////////////////////////



  private Coder<K> keyCoder;

  private Coder<V> valueCoder;



  private MapCoder(Coder<K> keyCoder, Coder<V> valueCoder) {

    this.keyCoder = keyCoder;

    this.valueCoder = valueCoder;

  }



  @Override

  public void encode(Map<K, V> map, OutputStream outStream) throws IOException, CoderException {

    encode(map, outStream, Context.NESTED);

  }



  @Override

  public void encode(Map<K, V> map, OutputStream outStream, Context context)

      throws IOException, CoderException {

    if (map == null) {

      throw new CoderException("cannot encode a null Map");

    }

    DataOutputStream dataOutStream = new DataOutputStream(outStream);



    int size = map.size();

    dataOutStream.writeInt(size);

    if (size == 0) {

      return;

    }



    // Since we handled size == 0 above, entry is guaranteed to exist before and after loop

    Iterator<Entry<K, V>> iterator = map.entrySet().iterator();

    Entry<K, V> entry = iterator.next();

    while (iterator.hasNext()) {

      keyCoder.encode(entry.getKey(), outStream);

      valueCoder.encode(entry.getValue(), outStream);

      entry = iterator.next();

    }



    keyCoder.encode(entry.getKey(), outStream);

    valueCoder.encode(entry.getValue(), outStream, context);

    // no flush needed as DataOutputStream does not buffer

  }



  @Override

  public Map<K, V> decode(InputStream inStream) throws IOException, CoderException {

    return decode(inStream, Context.NESTED);

  }



  @Override

  public Map<K, V> decode(InputStream inStream, Context context)

      throws IOException, CoderException {

    DataInputStream dataInStream = new DataInputStream(inStream);

    int size = dataInStream.readInt();

    if (size == 0) {

      return Collections.emptyMap();

    }



    Map<K, V> retval = Maps.newHashMapWithExpectedSize(size);

    for (int i = 0; i < size - 1; ++i) {

      K key = keyCoder.decode(inStream);

      V value = valueCoder.decode(inStream);

      retval.put(key, value);

    }



    K key = keyCoder.decode(inStream);

    V value = valueCoder.decode(inStream, context);

    retval.put(key, value);

    return retval;

  }



  /**

   * {@inheritDoc}

   *

   * @return a {@link List} containing the key coder at index 0 at the and value coder at index 1.

   */

  @Override

  public List<? extends Coder<?>> getCoderArguments() {

    return Arrays.asList(keyCoder, valueCoder);

  }



  /**

   * {@inheritDoc}

   *

   * @throws NonDeterministicException always. Not all maps have a deterministic encoding. For

   *     example, {@code HashMap} comparison does not depend on element order, so two {@code

   *     HashMap} instances may be equal but produce different encodings.

   */

  @Override

  public void verifyDeterministic() throws NonDeterministicException {

    throw new NonDeterministicException(

        this, "Ordering of entries in a Map may be non-deterministic.");

  }



  @Override

  public boolean consistentWithEquals() {

    return keyCoder.consistentWithEquals() && valueCoder.consistentWithEquals();

  }



  @Override

  public Object structuralValue(Map<K, V> value) {

    if (consistentWithEquals()) {

      return value;

    } else {

      Map<Object, Object> ret = Maps.newHashMapWithExpectedSize(value.size());

      for (Entry<K, V> entry : value.entrySet()) {

        ret.put(

            keyCoder.structuralValue(entry.getKey()), valueCoder.structuralValue(entry.getValue()));

      }

      return ret;

    }

  }



  @Override

  public void registerByteSizeObserver(Map<K, V> map, ElementByteSizeObserver observer)

      throws Exception {

    observer.update(4L);

    if (map.isEmpty()) {

      return;

    }

    Iterator<Entry<K, V>> entries = map.entrySet().iterator();

    Entry<K, V> entry = entries.next();

    while (entries.hasNext()) {

      keyCoder.registerByteSizeObserver(entry.getKey(), observer);

      valueCoder.registerByteSizeObserver(entry.getValue(), observer);

      entry = entries.next();

    }

    keyCoder.registerByteSizeObserver(entry.getKey(), observer);

    valueCoder.registerByteSizeObserver(entry.getValue(), observer);

  }



  @Override

  public TypeDescriptor<Map<K, V>> getEncodedTypeDescriptor() {

    return new TypeDescriptor<Map<K, V>>() {}.where(

            new TypeParameter<K>() {}, keyCoder.getEncodedTypeDescriptor())

        .where(new TypeParameter<V>() {}, valueCoder.getEncodedTypeDescriptor());

  }

}